<HTML>
<BODY BGCOLOR="white">
<PRE>
<FONT color="green">001</FONT>    <a name="line.1"></a>
<FONT color="green">002</FONT>    /*<a name="line.2"></a>
<FONT color="green">003</FONT>     * Copyright (C) 2008-2009 Archie L. Cobbs. All rights reserved.<a name="line.3"></a>
<FONT color="green">004</FONT>     *<a name="line.4"></a>
<FONT color="green">005</FONT>     * $Id: TopologicalSorter.html 4 2011-02-05 22:22:47Z archie.cobbs $<a name="line.5"></a>
<FONT color="green">006</FONT>     */<a name="line.6"></a>
<FONT color="green">007</FONT>    <a name="line.7"></a>
<FONT color="green">008</FONT>    package org.dellroad.stuff.graph;<a name="line.8"></a>
<FONT color="green">009</FONT>    <a name="line.9"></a>
<FONT color="green">010</FONT>    import java.util.ArrayList;<a name="line.10"></a>
<FONT color="green">011</FONT>    import java.util.Collection;<a name="line.11"></a>
<FONT color="green">012</FONT>    import java.util.Collections;<a name="line.12"></a>
<FONT color="green">013</FONT>    import java.util.Comparator;<a name="line.13"></a>
<FONT color="green">014</FONT>    import java.util.HashMap;<a name="line.14"></a>
<FONT color="green">015</FONT>    import java.util.List;<a name="line.15"></a>
<FONT color="green">016</FONT>    import java.util.Set;<a name="line.16"></a>
<FONT color="green">017</FONT>    <a name="line.17"></a>
<FONT color="green">018</FONT>    /**<a name="line.18"></a>
<FONT color="green">019</FONT>     * Topological sorting utility class.<a name="line.19"></a>
<FONT color="green">020</FONT>     */<a name="line.20"></a>
<FONT color="green">021</FONT>    public class TopologicalSorter&lt;E&gt; {<a name="line.21"></a>
<FONT color="green">022</FONT>    <a name="line.22"></a>
<FONT color="green">023</FONT>        private final Collection&lt;E&gt; nodes;<a name="line.23"></a>
<FONT color="green">024</FONT>        private final EdgeLister&lt;E&gt; edgeLister;<a name="line.24"></a>
<FONT color="green">025</FONT>        private final Comparator&lt;? super E&gt; tieBreaker;<a name="line.25"></a>
<FONT color="green">026</FONT>    <a name="line.26"></a>
<FONT color="green">027</FONT>        private HashMap&lt;E, Boolean&gt; visited;<a name="line.27"></a>
<FONT color="green">028</FONT>        private ArrayList&lt;E&gt; ordering;<a name="line.28"></a>
<FONT color="green">029</FONT>    <a name="line.29"></a>
<FONT color="green">030</FONT>        /**<a name="line.30"></a>
<FONT color="green">031</FONT>         * Primary constructor.<a name="line.31"></a>
<FONT color="green">032</FONT>         *<a name="line.32"></a>
<FONT color="green">033</FONT>         * @param nodes partially ordered nodes to be sorted<a name="line.33"></a>
<FONT color="green">034</FONT>         * @param edgeLister provides the edges defining the partial order<a name="line.34"></a>
<FONT color="green">035</FONT>         * @param tieBreaker used to sort nodes that are not otherwise ordered,<a name="line.35"></a>
<FONT color="green">036</FONT>         *  or null to tie break based on the original ordering<a name="line.36"></a>
<FONT color="green">037</FONT>         */<a name="line.37"></a>
<FONT color="green">038</FONT>        public TopologicalSorter(Collection&lt;E&gt; nodes, EdgeLister&lt;E&gt; edgeLister, Comparator&lt;? super E&gt; tieBreaker) {<a name="line.38"></a>
<FONT color="green">039</FONT>            this.nodes = nodes;<a name="line.39"></a>
<FONT color="green">040</FONT>            this.edgeLister = edgeLister;<a name="line.40"></a>
<FONT color="green">041</FONT>            if (tieBreaker == null)<a name="line.41"></a>
<FONT color="green">042</FONT>                tieBreaker = getDefaultTieBreaker();<a name="line.42"></a>
<FONT color="green">043</FONT>            this.tieBreaker = tieBreaker;<a name="line.43"></a>
<FONT color="green">044</FONT>        }<a name="line.44"></a>
<FONT color="green">045</FONT>    <a name="line.45"></a>
<FONT color="green">046</FONT>        /**<a name="line.46"></a>
<FONT color="green">047</FONT>         * Convenience constructor for when ties should be broken based on the original ordering.<a name="line.47"></a>
<FONT color="green">048</FONT>         *<a name="line.48"></a>
<FONT color="green">049</FONT>         * &lt;p&gt;<a name="line.49"></a>
<FONT color="green">050</FONT>         * Equivalent to:<a name="line.50"></a>
<FONT color="green">051</FONT>         *  &lt;blockquote&gt;<a name="line.51"></a>
<FONT color="green">052</FONT>         *  {@code TopologicalSorter(nodes, edgeLister, null);}<a name="line.52"></a>
<FONT color="green">053</FONT>         *  &lt;/blockquote&gt;<a name="line.53"></a>
<FONT color="green">054</FONT>         * &lt;/p&gt;<a name="line.54"></a>
<FONT color="green">055</FONT>         */<a name="line.55"></a>
<FONT color="green">056</FONT>        public TopologicalSorter(Collection&lt;E&gt; nodes, EdgeLister&lt;E&gt; edgeLister) {<a name="line.56"></a>
<FONT color="green">057</FONT>            this(nodes, edgeLister, null);<a name="line.57"></a>
<FONT color="green">058</FONT>        }<a name="line.58"></a>
<FONT color="green">059</FONT>    <a name="line.59"></a>
<FONT color="green">060</FONT>        /**<a name="line.60"></a>
<FONT color="green">061</FONT>         * Produce a total ordering of the nodes consistent with the partial ordering<a name="line.61"></a>
<FONT color="green">062</FONT>         * implied by the edge lister and tie breaker provided to the constructor.<a name="line.62"></a>
<FONT color="green">063</FONT>         *<a name="line.63"></a>
<FONT color="green">064</FONT>         * &lt;p&gt;<a name="line.64"></a>
<FONT color="green">065</FONT>         * The returned list will have the property that if there is an edge from X to Y,<a name="line.65"></a>
<FONT color="green">066</FONT>         * then X will appear before Y in the list. If there is no edge (or sequence of edges) from X to Y<a name="line.66"></a>
<FONT color="green">067</FONT>         * in either direction, then X will appear before Y if the tie breaker sorts X before Y.<a name="line.67"></a>
<FONT color="green">068</FONT>         * &lt;/p&gt;<a name="line.68"></a>
<FONT color="green">069</FONT>         *<a name="line.69"></a>
<FONT color="green">070</FONT>         * &lt;p&gt;<a name="line.70"></a>
<FONT color="green">071</FONT>         * This implementation runs in linear time in the number of nodes in the graph.<a name="line.71"></a>
<FONT color="green">072</FONT>         * &lt;/p&gt;<a name="line.72"></a>
<FONT color="green">073</FONT>         *<a name="line.73"></a>
<FONT color="green">074</FONT>         * @throws IllegalArgumentException if the partial ordering relation contains a cycle<a name="line.74"></a>
<FONT color="green">075</FONT>         */<a name="line.75"></a>
<FONT color="green">076</FONT>        public List&lt;E&gt; sort() {<a name="line.76"></a>
<FONT color="green">077</FONT>    <a name="line.77"></a>
<FONT color="green">078</FONT>            // Order nodes according to reverse tie breaker ordering<a name="line.78"></a>
<FONT color="green">079</FONT>            ArrayList&lt;E&gt; startList = Collections.list(Collections.enumeration(this.nodes));<a name="line.79"></a>
<FONT color="green">080</FONT>            Collections.sort(startList, getTieBreaker(true));<a name="line.80"></a>
<FONT color="green">081</FONT>    <a name="line.81"></a>
<FONT color="green">082</FONT>            // Perform depth-first search through nodes<a name="line.82"></a>
<FONT color="green">083</FONT>            this.visited = new HashMap&lt;E, Boolean&gt;(startList.size());<a name="line.83"></a>
<FONT color="green">084</FONT>            this.ordering = new ArrayList&lt;E&gt;(startList.size());<a name="line.84"></a>
<FONT color="green">085</FONT>            for (E node : startList)<a name="line.85"></a>
<FONT color="green">086</FONT>                visit(node, true);<a name="line.86"></a>
<FONT color="green">087</FONT>    <a name="line.87"></a>
<FONT color="green">088</FONT>            // Reverse list<a name="line.88"></a>
<FONT color="green">089</FONT>            Collections.reverse(this.ordering);<a name="line.89"></a>
<FONT color="green">090</FONT>            return this.ordering;<a name="line.90"></a>
<FONT color="green">091</FONT>        }<a name="line.91"></a>
<FONT color="green">092</FONT>    <a name="line.92"></a>
<FONT color="green">093</FONT>        /**<a name="line.93"></a>
<FONT color="green">094</FONT>         * Same as {@link #sort sort()} but treats all edges as reversed.<a name="line.94"></a>
<FONT color="green">095</FONT>         *<a name="line.95"></a>
<FONT color="green">096</FONT>         * &lt;p&gt;<a name="line.96"></a>
<FONT color="green">097</FONT>         * The returned list will have the property that if there is an edge from X to Y,<a name="line.97"></a>
<FONT color="green">098</FONT>         * then Y will appear before X in the list. If there is no edge (or sequence of edges) from X to Y<a name="line.98"></a>
<FONT color="green">099</FONT>         * in either direction, then X will appear before Y if the tie breaker sorts X before Y.<a name="line.99"></a>
<FONT color="green">100</FONT>         * &lt;/p&gt;<a name="line.100"></a>
<FONT color="green">101</FONT>         *<a name="line.101"></a>
<FONT color="green">102</FONT>         * @throws IllegalArgumentException if the partial ordering relation contains a cycle<a name="line.102"></a>
<FONT color="green">103</FONT>         */<a name="line.103"></a>
<FONT color="green">104</FONT>        public List&lt;E&gt; sortEdgesReversed() {<a name="line.104"></a>
<FONT color="green">105</FONT>    <a name="line.105"></a>
<FONT color="green">106</FONT>            // Order nodes according to normal tie breaker ordering<a name="line.106"></a>
<FONT color="green">107</FONT>            ArrayList&lt;E&gt; startList = Collections.list(Collections.enumeration(this.nodes));<a name="line.107"></a>
<FONT color="green">108</FONT>            Collections.sort(startList, getTieBreaker(false));<a name="line.108"></a>
<FONT color="green">109</FONT>    <a name="line.109"></a>
<FONT color="green">110</FONT>            // Perform depth-first search through nodes<a name="line.110"></a>
<FONT color="green">111</FONT>            this.visited = new HashMap&lt;E, Boolean&gt;(startList.size());<a name="line.111"></a>
<FONT color="green">112</FONT>            this.ordering = new ArrayList&lt;E&gt;(startList.size());<a name="line.112"></a>
<FONT color="green">113</FONT>            for (E node : startList)<a name="line.113"></a>
<FONT color="green">114</FONT>                visit(node, false);<a name="line.114"></a>
<FONT color="green">115</FONT>    <a name="line.115"></a>
<FONT color="green">116</FONT>            // Done<a name="line.116"></a>
<FONT color="green">117</FONT>            return this.ordering;<a name="line.117"></a>
<FONT color="green">118</FONT>        }<a name="line.118"></a>
<FONT color="green">119</FONT>    <a name="line.119"></a>
<FONT color="green">120</FONT>        private void visit(E node, boolean reverse) {<a name="line.120"></a>
<FONT color="green">121</FONT>    <a name="line.121"></a>
<FONT color="green">122</FONT>            // Have we been here before?<a name="line.122"></a>
<FONT color="green">123</FONT>            Boolean state = this.visited.get(node);<a name="line.123"></a>
<FONT color="green">124</FONT>            if (state != null) {<a name="line.124"></a>
<FONT color="green">125</FONT>                if (!state.booleanValue())<a name="line.125"></a>
<FONT color="green">126</FONT>                    throw new IllegalArgumentException("cycle in graph containing " + node);<a name="line.126"></a>
<FONT color="green">127</FONT>                return;<a name="line.127"></a>
<FONT color="green">128</FONT>            }<a name="line.128"></a>
<FONT color="green">129</FONT>            this.visited.put(node, false);<a name="line.129"></a>
<FONT color="green">130</FONT>    <a name="line.130"></a>
<FONT color="green">131</FONT>            // Get all destination nodes of all out-edges<a name="line.131"></a>
<FONT color="green">132</FONT>            ArrayList&lt;E&gt; targets = Collections.list(Collections.enumeration(this.edgeLister.getOutEdges(node)));<a name="line.132"></a>
<FONT color="green">133</FONT>    <a name="line.133"></a>
<FONT color="green">134</FONT>            // Sort them in reverse desired order and recurse<a name="line.134"></a>
<FONT color="green">135</FONT>            Collections.sort(targets, getTieBreaker(reverse));<a name="line.135"></a>
<FONT color="green">136</FONT>            for (E target : targets)<a name="line.136"></a>
<FONT color="green">137</FONT>                visit(target, reverse);<a name="line.137"></a>
<FONT color="green">138</FONT>    <a name="line.138"></a>
<FONT color="green">139</FONT>            // Add this node to list in post-order and mark complete<a name="line.139"></a>
<FONT color="green">140</FONT>            this.ordering.add(node);<a name="line.140"></a>
<FONT color="green">141</FONT>            this.visited.put(node, true);<a name="line.141"></a>
<FONT color="green">142</FONT>        }<a name="line.142"></a>
<FONT color="green">143</FONT>    <a name="line.143"></a>
<FONT color="green">144</FONT>        private Comparator&lt;? super E&gt; getDefaultTieBreaker() {<a name="line.144"></a>
<FONT color="green">145</FONT>            final HashMap&lt;E, Integer&gt; orderMap = new HashMap&lt;E, Integer&gt;(this.nodes.size());<a name="line.145"></a>
<FONT color="green">146</FONT>            int posn = 0;<a name="line.146"></a>
<FONT color="green">147</FONT>            for (E node : this.nodes)<a name="line.147"></a>
<FONT color="green">148</FONT>                orderMap.put(node, posn++);<a name="line.148"></a>
<FONT color="green">149</FONT>            return new Comparator&lt;E&gt;() {<a name="line.149"></a>
<FONT color="green">150</FONT>                public int compare(E node1, E node2) {<a name="line.150"></a>
<FONT color="green">151</FONT>                    return orderMap.get(node1) - orderMap.get(node2);<a name="line.151"></a>
<FONT color="green">152</FONT>                }<a name="line.152"></a>
<FONT color="green">153</FONT>            };<a name="line.153"></a>
<FONT color="green">154</FONT>        }<a name="line.154"></a>
<FONT color="green">155</FONT>    <a name="line.155"></a>
<FONT color="green">156</FONT>        private Comparator&lt;? super E&gt; getTieBreaker(boolean reverse) {<a name="line.156"></a>
<FONT color="green">157</FONT>            if (reverse)<a name="line.157"></a>
<FONT color="green">158</FONT>                return Collections.reverseOrder(this.tieBreaker);<a name="line.158"></a>
<FONT color="green">159</FONT>            return this.tieBreaker;<a name="line.159"></a>
<FONT color="green">160</FONT>        }<a name="line.160"></a>
<FONT color="green">161</FONT>    <a name="line.161"></a>
<FONT color="green">162</FONT>        /**<a name="line.162"></a>
<FONT color="green">163</FONT>         * Implemented by classes that can enumerate the outgoing edges from a node in a graph.<a name="line.163"></a>
<FONT color="green">164</FONT>         */<a name="line.164"></a>
<FONT color="green">165</FONT>        public static interface EdgeLister&lt;E&gt; {<a name="line.165"></a>
<FONT color="green">166</FONT>    <a name="line.166"></a>
<FONT color="green">167</FONT>            /**<a name="line.167"></a>
<FONT color="green">168</FONT>             * Get the set of all nodes X for which there is an edge from {@code node} to X.<a name="line.168"></a>
<FONT color="green">169</FONT>             */<a name="line.169"></a>
<FONT color="green">170</FONT>            Set&lt;E&gt; getOutEdges(E node);<a name="line.170"></a>
<FONT color="green">171</FONT>        }<a name="line.171"></a>
<FONT color="green">172</FONT>    }<a name="line.172"></a>
<FONT color="green">173</FONT>    <a name="line.173"></a>




























































</PRE>
</BODY>
</HTML>
